Thermal responsive switching device



March 17, 1959 R. w. GUSTAFSON ETAL 2, 7

THERMAL RESPONSIVE SWITCHING DEVICE Filed Nov. 27, 1957 .mmm II INVENTORS RALPH W. GUSTAFSQN,

BY WILEY M. Humnfzx.

%a4Z: MOM/ vATTORNEY United States Patent THERMAL RESPONSIVE SWITCHING DEVICE Ralph W. Gustafson, Morrison, and Wiley M. Hummel,

Prophetstown, Ill., assignors to General Electric Company, a corporation of New York Application November 27, 1957, Serial No. 699,386

9 Claims. (Cl. 200-138) the plenum chamber of the furnace, to control the operation of the fan which circulates the warmed air throughout the area to be heated. In addition, this plenum chamber contains a second control device which will turn off the burner at a predetermined upper temperature in the event that the air temperature exceeds a safe value. The general nature of this control system and typical prior art devices are shown and described in U. S. Patent 2,752,455 to Morris W. Carlson, assigned to the assignee of the present application. A single control device which performs these two control functions is normally referred to as a fan and limit control.

The prior art devices have, in general, utilized many distinct specially constructed parts and have required complex linkages to transform the force developed by the thermosensitive element into a force to operate a switch. These devices have been expensive and difiicult to manufacture, install, and service. Previous elforts to overcome these disadvantages have generally produced unreliable devices.

It is therefore an object of this invention to provide a switching device which is simple and economical in construction but which provides reliable and accurate control.

It is another object of this invention to provide a reliable fan and limit control having a common mounting for separate and independently actuated switches, such switches and their actuating mechanisms having substantial part-by-part identity.

It is another object of this invention to provide a control device having an adjustable thermal sensitive actuating mechanism which will provide accurate and reliable control when utilized with conventional snap-acting self-contained switching devices.

It is a still further object of this invention to provide a fan and limit control which is not only rugged and reliable in use but which can be shipped and stored with a minimum of extra care.

In furtherance of these objects and in accordance with one aspect of our invention, we provide at least one rigidly mounted switch and a bimetal actuator having one end operatively connected to the switch. The other end of the bimetal is carried by a carriage member which is supported on and movable relative to the rigid mounting and is provided with an adjusting screw which bears against the rigid mounting so as to permit adjustment of the temperature at which the bimetals will actuate the switch. The carriage adjusting screws preferably operate against a manually rotatable cam so as to provide for easy adjustment of the actuating temperature in the field.

Further objects and advantages of this invention will become apparent and the invention will be better understood by reference to the following description and the accompanying drawings; the features of novelty which 2,878,344 Patented Mar. 17, 1959 characterize this invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In the drawing,

Figure 1 is a front view of the assembled device;

Figure 2 is a sectional view of the assembled device taken at the point 2--2 of Figure 1;

Figure 3 is a bottom view of the device along the line 3-3 of Figure 1;

Figure 4 is a cutaway view showing the fan switch with its manual adjusting mechanism at the low temperature position; and

Figure 5 is a cutaway view showing the limit switch portion of applicants device.

Referring to Figures 1, 2 and 3, it is seen that an enclosing case 1 is held against a frame or member 2 by the fastening means shown generally at 3. This switching device is normally installed so that the frame 2 abuts a side wall of a plenum chamber in a hot air furnace so that a first bimetal 4 (hereinafter called the fan bimetal) and a second bimetal 5 (hereinafter called the limit bimetal) extend external to the frame 2 and are enveloped by the air to be heated. A bracket 6 is attached to frame 2 and rigidly supports a fan switch 7 and a limit switch 8 through the action of mounting bolts 9; the switches being mounted so that an outwardly biased operating button 10 for fan switch 7 and an outwardly biased operating button 11 for limit switch 8 are disposed towards frame 2.

Referring now to Figures 3 and 4, it is seen that the fan bimetal 4 is rigidly attached to the end 12 of a carriage member 13. The carriage member 13 passes through respective apertures 2a and 6a in frame 2 and bracket 6 which apertures are relatively located so that a portion of carriage member 13 is located in the space between the switches 7 and 8. It is to be noted that a carriage member 22 (see Figure 5) also passes through apertures 2a and 6a so that both carriage members slide against and help support each other. The end 14 of the carriage member 13 extends beyond the bracket 6 and carries thereon an adjustable screw 15. This screw bears against the cam 16 which is mounted for rotation with the shaft 17; the position of this cam is both controlled and indicated by the knob 18 which carries a pointer that cooperates with temperature indications on the enclosing case 2 (see Figure 1). The spring 20 acts between the frame 2 and the end 12 of the carriage member and serves to bias the end 12 away from the frame 2. The free end of the bimetal 4 is attached to the right hand end of the rod 19 whose left hand end is in operative engagement with the fan switch operating button 10.

The left hand end of rod 19, which bears against the operating button 10, has an enlarged conical end portion 21; this enlarged portion eliminates sliding friction between the rod 19 and the frame 2. As is seen in Figure 4, when the bimetal 4 is in its open position (solid lines) the enlarged conical end portion 21 rests against that portion of the frame defining the bottom of the aperture 2b shown in dotted lines. In the rest position, the main body of rod 19 is raised so that as the bimetal closes to the position shown in dotted lines, the shank portion 21 will engage the operating button 10 so as to suspend the rod 19 free of the frame between the bimetal closing force and the switch operating button bias. Because of this suspension, there is no sliding friction between rod 19 and the frame to disturb the temperature calibration.

Referring to Figure 5, it can be seen that the construction of the limit switch section of this invention is very similar to that of the fan switch section just described. The limit bimetal 5 is rigidly attached to the end 29 of the carriage member 22 whose end 23 carries an ad justable screw 24 which bears against the bracket 6. The

spring 25 acts between the frame 2 and the end 29 so as to bias the carriage away from the switch 8. The other end of the bimetal 5 is connected to the operating rod 26 whose other end bears against the limit switch operating button 11. It is noted that the end 27 of the operating rod is conic'ally enlarged so as to reduce friction between the rod and the frame member 2 as was explained for the fan switch.

In operation, it is seen that the fan bimetal 4, which is arranged to open with increasing temperature, allows the operating rod 19 to move to the right as temperature increases so that the switch contacts 30 will move from its dotted position (see Figure 4.) to the solid position so as to close the circuit with contact 28; that is, the switch 7 is a normally closed switch whose contact bias is allowed to close the switch as the operating rod 19 moves to the right with increasing temperature which opens the bimetal. The screw 15 which bears against the cam 16, is a factory adjust screw which positions the carriage 13 relative to the cam surface and thereby adjusts the position of the fan bimetal 4 relative to the fan switch 7 so as to determine the operating limit temperatures for this switch. The rotatable cam surface 16 provides customer adjustment and enables the customer to determine the temperature between the factory limits at which he desires the switch to operate and thereby energize the fan.

As is seen from the previous description, the fan switch mechanism and the limit switch mechanism are substantially identical. Two important dilferences exist however; the first of these relates to the limit bimetal 5 which closes upon increasing heat whereas the fan bimetal 4 opens upon increasing heat; in addition, the adjusting screw 24 of the limit switch bears against the bracket 6 and may be called a fixed adjustment whereas the adjustment screw 15 of the fan switch bears against a cam surface and thus is adjustable by the customer. However, both switches are of the normally closed type and all other parts are substantially identical even to the bimetals with the exception of the direction of bending.

The mode of operation of the limit switch is similar to that of the fan switch. As is seen in Figure 5, when the temperature increases, the bimetal closes so as to move the operating rod 26 against the switch operating button 11 and thereby open the switch and disconnect the burner apparatus. It is apparent however that an additional cam and operating shaft and knob could be added to the bracket 6 and thereby render the temperature adjust of the limit switch variable within the pre-set factory limits as determined by the adjusting screw 24 much in the same manner as is done for the fan switch.

The previously described structures and concepts make it possible to utilize different types of unitary switches in applicants device including the inexpensive appliance switches. The appliance switches often have small operating force tolerances at the actual trip and reset points but have wide operating force tolerances at the free position of the operating plunger. For actuation of this type of switch, it is therefore necessary to select a bimetal having a force gradient which will keep the tolerances on temperature dilferential of switch operation within specified limits, for example: i5 Fahrenheit. With such proper selection, the bimetal will cause a desired gradual movement of the switch plunger between the trip and reset positions with a gradual change in bimetal temperature.

It is apparent from the foregoing description that the disclosed device satisfies all of the stated objects and that the obstacles which have been surmounted in its design and construction justify its acceptance as a commercially successful fan and limit furnace control.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. Temperature 'responsiveheating control apparatus arranged to be mounted on the wall of a furnace chamher, comprising a frame, a switch fixedly mounted on said frame and including a movable actuating member, an elongated carriage member supported on said frame for longitudinal movement relative thereto, said carriage member having an outer portion extending beyond said frame for accommodation within said furnace chamber, a bimetal mounted on said carriage member for sensing the temperature within said chamber, said bimetal having a fixed end secured to said outer portion of said carriage member and a free end for operating said switch, a movable operating rod connecting said free end of said bimetal to said actuating member of said switch, a cam member rotatably mounted on said frame, a protection on said carriage at its end remote from said bimetal and resilient means biasing said carriage member to bring said protection into contact with said cam member, whereby said cam is effective to vary the position of said carriage member and said bimetal to control the temperature at which said switch is operated.

2. Temperature responsive apparatus for use in a heating system comprising a frame, a unitary switch, mounting means rigidly positioning said switch on one side of said frame, an elongated carriage member supported by and movable relative to said mounting means and frame and extending on both sides of said frame, a bimetal having one end fixed to said carriage member at a point on the side opposite to said switch, means operatively connecting the other end of said bimetal with said switch, and means for adjusting the longitudinal position of said carriage relative to said frame and mounting means, there- 'by to adjust the position of said bimetal and the temperature at which said switch is actuated by said bimetal.

3. The temperature responsive apparatus as set forth in claim 2 wherein the means for adjusting the longitudinal position of the carriage comprises a cam member Totatably fastened to said mounting means, a projection on said carriage member in contact with said cam member and resilient means biasing said carriage away from said switch and said projection into engagement with said cam member.

4. Switching apparatus for use in a heating system comprising a frame having an aperture therein, a switch, mounting means rigidly positioning said switch relative to said frame and having an aperture therein opposite said frame aperture, a carriage having a portion thereof passing through said frame aperture and said mounting means aperture and having a projection thereon adjacent to said mounting means, a U-shaped bimetal having one end fixed to said carriage, means operatively connecting the upper end of said bimetal with said switch, means for biasing said carriage away from said switch, and a cam member rotatably fastened to said mounting means and in engagement with said carriage projection whereby rotation of said cam will adjust the position of said carriage and said bimetal and thereby the temperature at which said switch is actuated by said bimetal.

5. Switching apparatus for use in a hot air heating system comprising a frame, a first switch for controlling the air circulating fan, a second switch for controlling the fuel supply, means for mounting said first and second switches on said frame, a first carriage supported by and movable relative to said frame, a bimetal having one end attached to said first carriage and its other end operatively connected to said first switch whereby movement of said bimetal in response to temperature changes of the air to be heated will control the air circulating fan, a second bimetal having one end attached to said second carriage and its other end operatively connected to said second switch, whereby movement of said second bimetal in response to the temperature changes of the air being heated will control the supply of fuel, and means for adjusting the position of said carriages relative to said frame to thereby adjust the position of said bimetals relative to said switches for controlling the temperatures at which said bimetals actuate said switches.

6. The switching apparatus as set forth in claim 5 wherein the means for adjusting the position of said carriages includes projections on said first and second carriages, means biasing said carriages away from said first and second switches and longitudinally adjustable threaded members on said projections in engagement with said mounting means.

7. Switching apparatus for use in a heating system comprising a frame having an aperture therein, a switch having a biased operating member, mounting means rigidly positioning said switch relative to said frame, a carriage member mounted on said frame and movable relative thereto, a U-shaped bimetal having one end fixed to said carriage member, and a rod having one end operatively connected to the other end of said bimetal and hav-' ing its other end free and positioned to engage the biased operating member of said switch, said rod having an enlarged tapered shank portion engaging the wall of said frame defining said aperture when said U-shaped bimetal is open, said rod being suspended free of said frame between said bimetal and said biased switch operating member when said U-shaped bimetal is closed.

8. Temperature responsive heating control apparatus arranged to be mounted on the wall of a furnace chamber, comprising a frame, a switch fixedly mounted on said frame and having a movable operating member, an elongated carriage member supported on said frame for longitudinal movement relative thereto, said carriage member having an outer portion extending beyond said frame for accommodation within said furnace chamber, a bimetal mounted on said carriage member for sensing the temperature within said chamber, said bimetal having a fixed end secured to the outer portion of said carriage member and a free end for operating said switch, a movable operating rod for actuating said operating member of said switch from said free end of said bimetal, said rod having one end connected to said free end of said bimetal and having its other end free and positioned to engage the said operating member of said switch, said rod having an enlarged tapered shank portion engaging said frame when said bimetal is in a first position, said rod being suspended free of said frame between said bimetal and said switch operating member when said bimetal is in a second position, and means engaging said carriage member at its end remote from said bimetal for adjusting the longitudinal position of said carriage relative to said frame thereby to adjust the position of said bimetal relative to said switch operating member to control the temperature at which said switch is operated.

9. Control apparatus arranged for mounting on the wall of a furnace chamber for controlling a fuel supply valve and an air circulating fan associated with said furnace, comprising a frame, a first switch for controlling the air circulating fan, a second switch for controlling the fuel supply valve, means for mounting said first and second switches fixedly on said frame, first and second elongated carriage members supported by said frame for longitudinal movement relative thereto, a first bimetal having a fixed end secured to said first carriage member and a free end for operating said first switch, a second bimetal having a fixed end secured to said second carriage member and a free end for operating said second switch, said first and second bimetals responding oppositely to temperature changes within said chamber whereby said first bimetal fiexes to open said first switch and second bimetal flexes to close said second switch as the temperature in said chamber rises, and means for independently adjusting the position of said carriages relative to said frame thereby to adjust the position of said bimetals relative to said switches and control the temperatures at which said himetals actuate said switches.

References Cited in the file of this patent UNITED STATES PATENTS 2,192,633 Beam Mar. 5, 1940 2,489,854 Brockman Nov. 29, 1949 2,774,847 Ray et al Dec. 18, 1956 

